<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
    
  </style>
</head>
<body>
  
</body>
<script>

  var str = "hello js"

  console.log( str )
  console.log( str )

  var qfVar = 10;
  console.log(qfVar)

  var a;
  console.log(a)

  var b = null
  console.log(b)

  var c = 10, d = 20, e = 30;
  console.log(c, d, e, str, qfVar);

  c = "hello";
  console.log(c);
  
</script>
</html>